The present invention relates to an air suspension, and more particularly to a method for retaining the air suspension in a fixed condition when the vehicle is lifted and the air suspension is in an unloaded condition.
A common air suspension system typically comprises a chassis of a vehicle and a longitudinal member extending generally lengthwise of the vehicle for pivoting about an axis generally transverse of the vehicle. The longitudinal member carries an axle having one or more road wheels. An air spring having a piston and an air cell is mounted spaced from the axis and act as an adjustable compression spring between the vehicle and the longitudinal member to bias the wheels for effective road engagement and to buffer axle and wheel vibration.
Vehicles fitted with an air suspension are sometimes used without being inflated such as when being transported on railroad cars. At other times the vehicle axles are left to hang away from the chassis in an unloaded condition on the wheels such as when the vehicle is lifted on and off a ship. These operations cause the air spring to extend without air and pull away from the piston causing the air cell to xe2x80x9csnap throughxe2x80x9d or invert. Once the air cell inverts, the air spring may have difficulty being correctly inflated. Further, if a load is again placed on the suspension while the air cell is inverted, the air spring is compressed and the air cell may become trapped between the piston and upper mounting resulting in damage to the air cell.
Accordingly, it is desirable to provide a method of retaining the air suspension in a fixed condition when the vehicle is lifted and the air suspension is in an unloaded condition to prevent inversion and the resultant damage to the air spring.
The air suspension according to the present invention includes an air spring having an air cell and a piston which act as a compression spring between a longitudinal member and a chassis component. The air cell is powered by the piston which is actuated by a gas feed connected to the vehicle air supply. Preferably, a bottom of the piston is attached to the longitudinal member and the air cell is attached to a top of the piston.
When there is no pressure in the air spring, the air cell is deflated and the suspension is mechanically bottomed out. The invention introduces a negative pressure into the air cell at this condition. A partial vacuum is formed and the air cell collapses in upon itself. The collapsed air cell grips the piston thereby immobilizing the air spring.
As the piston is attached to the longitudinal member and the air cell to the chassis component, the longitudinal member is retained in a substantially fixed position relative to the chassis component. Accordingly, when the vehicle is lifted and the air suspension becomes unloaded, the longitudinal member is maintained relative to the chassis component by the immobilized air spring to thereby prevent the air cell from being inverted and damaged.
In one embodiment, a switch is contracted when the piston bottoms out. The switch actuates the vacuum source. A vehicle having an air suspension is also commonly fitted with an anti-vacuum system. The present invention closes the anti-vacuum system prior to providing a negative pressure within the air cell. The anti-vacuum system is thus prevented from interfering with the desired collapsed condition within the air cell.